SAN DIEGO, April 5, 2011 /PRNewswire/ – Optimer Pharmaceuticals, Inc. (NASDAQ: OPTR) announced today that the U.S. Food and Drug Administration’s (FDA) Anti-Infective Drugs Advisory Committee (AIDAC) recommended that the FDA approve Optimer’s investigational antibiotic DIFICID(TM)(fidaxomicin) for the treatment of patients with Clostridium difficile infection (CDI), a bacterial infection in the lining of the gut that can cause severe diarrhea, colitis and in some cases death. In a unanimous 13-0 decision, the AIDAC found that the clinical evidence submitted by Optimer demonstrated the safety and effectiveness of DIFICID for the treatment of CDI.

“We view the vote of the FDA’s panel of expert advisors, with diverse backgrounds ranging from infectious disease to biostatistics, as a strong endorsement for approving DIFICID for the treatment of CDI. We are encouraged that the advisory committee recognizes the urgent need for new treatment options for CDI and the seriousness of the increasing incidence of these infections,” said Pedro Lichtinger, President and CEO of Optimer. “We are proud to be one step closer to providing patients, healthcare providers and physicians with a new treatment option for CDI, a serious and debilitating disease that can impact every aspect of a patient’s life.”

The FDA is not bound by the committee’s guidance but takes its advice into consideration. Optimer submitted its New Drug Application (NDA) for DIFICID on November 30, 2010. The FDA accepted the DIFICID NDA filing and granted a six-month Priority Review in January 2011, assigning a Prescription Drug User Fee Act (PDUFA) goal date of May 30, 2011.

“In Phase 3 clinical studies, DIFICID was proven to be as effective as vancomycin in clinical cure, and was superior to vancomycin in global cure, defined as cure without a recurrence after 4 weeks of therapy. The advisory committee referred to the global cure outcome as 30-day resolution, which we believe is indicative of DIFICID’s benefit in reducing recurrences,” said Sherwood Gorbach, M.D., Optimer’s Chief Medical Officer. “While the advisory committee vote was split on how best to describe the recurrence benefit, the committee members overwhelmingly recognized that DIFICID at 30 days was superior to vancomycin. We appreciated the committee’s discussion and look forward to working with the FDA as it considers our DIFICID NDA.”

The AIDAC based its decision in part on the review of clinical evidence from the two largest, comparative Phase 3 clinical trials ever conducted against vancomycin in CDI. These multi-center, randomized, double-blind trials enrolled a total of 1,164 adults with confirmed CDI, who received either DIFICID (200 mg q12h) or vancomycin (125 mg q6h), the only FDA-approved product for the treatment of CDI. The objective of both studies was to show that a 10-day course of DIFICID was at least as efficacious (non-inferior) and safe as a 10-day course of vancomycin for the treatment of CDI. In both studies, DIFICID demonstrated a statistically significant reduction in the rate of recurrence compared with patients treated with vancomycin, reducing CDI recurrences by 47 percent, and was statistically superior to vancomycin in global cure rate (clinical cure without disease recurrence within four weeks). In addition, DIFICID met the primary endpoint of non-inferiority of clinical cure (defined as patients requiring no further CDI therapy two days after completion of study medication) compared to vancomycin.

DIFICID was safe and well tolerated in both studies, showing a similar incidence of treatment-related adverse events when compared to vancomycin.

Scheduled Conference Call

Optimer will host a conference call tomorrow at 8:00 a.m. Eastern Time (5:00 a.m. Pacific Time) to discuss this announcement. To participate in the conference call, please dial (877) 280-7280 from the U.S., or (678) 825-8232 for international callers. Please specify to the operator that you would like to join “Optimer’s Conference Call.” The conference call will be webcast live under the Investors section of Optimer’s website at www.optimerpharma.com, where it will be archived for 30 days following the call. Please connect to Optimer’s website several minutes prior to the start of the broadcast to ensure adequate time for any software download that may be necessary.

About DIFICID(TM) (Fidaxomicin)

DIFICID(TM) (fidaxomicin) is a new antibiotic with a novel mechanism of action, which inhibits the bacterial enzyme RNA polymerase, resulting in the rapid killing of C. difficile. The narrow-spectrum profile of DIFICID eradicates C. difficile selectively with minimal disruption to the normal intestinal flora, while the alternative antibiotics used to treat CDI, metronidazole and vancomycin, have been shown to disrupt the gut flora. DIFICID facilitates the return of normal physiological conditions in the colon which may be responsible for reducing CDI recurrence rates. In two Phase 3 trials for the treatment of CDI, DIFICID was equally effective in clinical cure when compared to vancomycin, the only FDA approved product for CDI. DIFICID also demonstrated statistically significant reduction in recurrences and an increase in global cure rate, defined as cure without recurrence. Importantly, DIFICID reduced the risk of recurrence by 47% compared to vancomycin. TheNew England Journal of Medicine has published results from the first Phase 3 trial in an article titled, “Fidaxomicin versus Vancomycin for Clostridium difficile Infection,” which appeared in the February 3, 2011 issue.

About Clostridium difficile Infection (CDI)

Clostridium difficile infection (CDI), commonly referred to as “C. difficile” or “c-diff”, has become a significant medical problem in hospitals, long-term care facilities, and in the community and is estimated to afflict more than 700,000 people each year in the U.S. It is a serious illness resulting from infection of the inner lining of the colon by C. difficile bacteria, which produce toxins that cause inflammation of the colon, severe diarrhea and, in the most serious cases, death. Patients typically develop CDI from the use of broad-spectrum antibiotics that disrupt normal gastrointestinal (gut) flora, thus allowing C. difficile bacteria to flourish and produce toxins.

Current therapeutic options for CDI include the off-label use of metronidazole and oral vancomycin, the latter being the only FDA-approved treatment. However, approximately 20% to 30% of CDI patients who initially respond to these treatments experience a clinical recurrence following cessation of the CDI treatment.

Primary risk factors for CDI include broad-spectrum antibiotic use (such as cephalosporins and fluoroquinolones), older age (over 65) and exposure to emerging hyper-virulent strains (BI/NAP1/027, 078, 001) of C. difficile. The rise in incidence of CDI, along with high rates of both treatment failures and recurrences with current therapies has resulted in greater awareness and concern about CDI among medical professionals and public health officials. Advancing age is one of the most significant risk factors for CDI and with the 65-plus population growing every year in the US, the incidence of CDI has the potential to increase in hospitals and long-term care facilities. You may learn more about CDI at www.cdiinfo.org, a website of Optimer.

About Optimer

Optimer Pharmaceuticals, Inc. is a biopharmaceutical company focused on discovering, developing and commercializing innovative hospital specialty products that have a positive impact on society. Optimer has two anti-infective product candidates in development, DIFICID(TM) (fidaxomicin) and Pruvel(TM) (prulifloxacin). DIFICID is a narrow spectrum antibiotic being developed for the treatment of Clostridium difficile infection (CDI). The FDA granted the Company’s request for six-month Priority Review of DIFICID, and has assigned a Prescription Drug User Fee Act (PDUFA) goal date of May 30, 2011. The Company also filed a MAA with the European Medicines Agency (EMA) for DIFICID. Pruvel(TM) is a prodrug in the fluoroquinolone class of antibiotics being developed as a treatment for infectious diarrhea. Additional information can be found at http://www.optimerpharma.com.

Forward Looking Statements

Statements included in this press release that are not a description of historical facts are forward-looking statements, including without limitation statements related to expected DIFICID(TM) increases in the U.S. population over age 65 and the incidence of CDI, DIFICID potential regulatory approval of DIFICID, and the awareness of CDI among healthcare professionals. Words such as “believes,” “would,” “anticipates,” “plans,” “expects,” “may,” “intend,” “will,” and similar expressions are intended to identify forward-looking statements. The inclusion of forward-looking statements should not be regarded as a representation by Optimer that any of its plans will be achieved. Actual results may differ materially from those set forth in this release due to the risks and uncertainties inherent in Optimer’s business including, without limitation, risks relating to: the development of alternative treatments for or means of preventing CDI, whether regulatory authorities will review or approve Optimer’s applications for marketing approval within Optimer’s anticipated timelines or at all, the timing of any marketing approvals DIFICID and other risks detailed in Optimer’s filings with the Securities and Exchange Commission.